cannot convert a zookeeper object to json and vice versa

Question

Hello everyone i have a simple problem where i cant seem to convert a zookeeper object into json and vice versa using GSON library in jersey for java web services.The error i get is

Exception in thread "main" java.lang.StackOverflowError
    at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:381)
    at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:376)
    at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:381)
    at com.google.gson.internal.$Gson$Types.resolve($Gson$Types.java:376)

and it keeps going on pretty large. From what i have searched this semms to be the issue of too deeply nested objects and recursion. Here's what i tried for a simple POC

ZooKeeper zoo;
        try {
            zoo = new ZooKeeper("localhost:2182",5000,null);
            String obj=gson.toJson(zoo, ZooKeeper.class);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

can someone clearly explain what is the actual problem and even if its possible to convert and use zookeeper objects as json(because of all the threads associated with it)

Possible duplicate. https://stackoverflow.com/questions/10209959/gson-tojson-throws-stackoverflowerror — Januson, Mar 01 '19 at 07:27
Problem is, the error message isn't very clear on where the circular reference occurs, and the class to check is over 3K lines of code. — Stultuske, Mar 01 '19 at 07:51
well i have had a look and the logger is declared as static so we can rule that one out i suppose? — JayD, Mar 01 '19 at 07:56
@JayD, have you fixed that bug? If yes, could you share details? — Michał Ziober, Mar 01 '19 at 15:03
@MichałZiober unfortunately no.I guess i agree with DEV-Jacol's approach.. — JayD, Mar 04 '19 at 05:50

DEV-Jacol · Accepted Answer · 2019-03-04T07:49:27.653

ZooKeeper is a server and not a DTO

maybe you want to do a json with DTO configuration

my proposition

public static void main(String[] args) {
  ZooKeeper zoo;
  try {
    ZooKeeperConfDTO conf = new ZooKeeperConfDTO("localhost:2182", 5000, null);
    zoo = runZoo(conf);
    String json = new Gson().toJson(conf);
    System.out.println(json); //---->{"connectString":"localhost:2182","sessionTimeout":5000}
  } catch (Exception e) {
    e.printStackTrace();
  }
}

private static ZooKeeper runZoo(ZooKeeperConfDTO conf) throws IOException {
  return new ZooKeeper(conf.connectString, conf.sessionTimeout, conf.watcher);
}

and created class

import org.apache.zookeeper.Watcher;

public class ZooKeeperConfDTO {
  public String connectString;
  public int sessionTimeout;
  public Watcher watcher;

  public ZooKeeperConfDTO(String connectString, int sessionTimeout, Watcher watcher) {
    this.connectString = connectString;
    this.sessionTimeout = sessionTimeout;
    this.watcher = watcher;
  }
}

version 2:

create your TypeAdapter for ClientCnxn

import java.io.IOException;
import org.apache.zookeeper.ClientCnxn;
import com.google.gson.TypeAdapter;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonWriter;

public class ClientCnxnAdapter extends TypeAdapter<ClientCnxn> {
    @Override
    public void write(JsonWriter writer, ClientCnxn cnxn) throws IOException {
        writer.beginObject();
        writer.name("sessionId");
        writer.value(cnxn.getSessionId());
        writer.name("timeOut");
        writer.value(cnxn.getSessionTimeout());
        writer.endObject();
    }

    @Override
    public ClientCnxn read(JsonReader in) throws IOException {
        return null;
    }
}

and use it

public static void main(String[] args) {
    ZooKeeper zoo;
    try {
        zoo = new ZooKeeper("localhost:2182", 5000, null);
        Gson gson = new GsonBuilder().registerTypeAdapter(ClientCnxn.class, new ClientCnxnAdapter()).create() ;
        String json = gson.toJson(zoo);
        System.out.println(json); //---->{"cnxn":{"sessionId":0,"timeOut":0},"watchManager":{"dataWatches":{},"existWatches":{},"childWatches":{}}}
    } catch (Exception e) {
        e.printStackTrace();
    }
}

what i meant was that the zookeeper object has all the references for the state of the client such as Connected,disconnected expired and etc but with your approach i wont have access to all those settings will i? Anyways i have dropped that approach now but thanks for answering — JayD, Mar 04 '19 at 06:02

cannot convert a zookeeper object to json and vice versa

1 Answers1